1. Field of the Invention
The invention relates to synthetically generated displays and particularly to cathode ray tube displays utilizing stroke (caligraphic) techniques.
2. Description of the Prior Art
Stroke written CRT displays involve deflecting the electron beam in a manner so as to actually "draw" the shape of figures to be presented. This differs from a raster type system in which the beam traces an unchanging pattern of scan lines and information is presented by illuminating the beam at the appropriate points along each line. Inherent to raster systems is a display refresh rate that is independent of the amount of information to be presented. In a stroke system the time required to present all the information is directly proportional to the amount of information.
Refresh rate is defined as the number of times per second a display format is presented for viewing. A sufficiently high refresh rate is desirable to avoid effects such as flicker. When a fixed refresh rate is used, this implies a fixed time interval in which all information may be presented. If more information is required than can be written in the fixed interval at a given writing speed, the additional information could be truncated from the display. In many applications, and significantly in the case of aircraft flight instruments, loss of such information is unacceptable.
Increasing the stroke writing speed is a method which has been used to increase the amount of information which can be displayed in a given time interval. This method has several disadvantages. First, CRT display deflection bandwidth can be exceeded by increasing writing speed. This can result in severe degradation of quality and integrity of the displayed information. Also, in environments where power dissipation is critical, higher writing speed can result in an unacceptable increase in deflection power.